Hydraulic percussion device with pressure-responsive control of impact frequency

ABSTRACT

A hydraulic percussion device has a reciprocating ram with a smaller rearwardly facing land and a larger forwardly facing land, the former being continuously subjected to the supply pressure of a fluid source whereas the latter is alternately connectable to a low-pressure discharge line (for the forward stroke) and to a branch of a conduit carrying the supply pressure (for the return stroke) by a slide valve whose shifting is hydraulically controlled by the ram. A throttle valve in the branch conduit leading to the slide valve senses the supply pressure and, if that pressure falls below a predetermined level, partly blocks that branch so as to reduce the reverse pressure differential effective during the return stroke whereby the withdrawal of the ram from an impact-receiving tool is delayed so that the impact frequency decreases, thus reducing the demand upon the source and providng more time for the buildup of the requisite working pressure.

United States Patent 1 1 Arndt NOV. 27, 1973 HYDRAULIC PERCUSSION DEVICE WITH PRESSURE-RESPONSIVE CONTROL OF IMPACT FREQUENCY Appl. No.: 143,400

' Primary Examiner-Paul E. Maslousky Attorney-Kar] F. Ross ABSTRACT A hydraulic percussion device has a reciprocating ram with a smaller rearwardly facing land and a larger forwardly facing land, the former being continuously subjected to the supply pressure of a fluid source whereas the latter is alternately connectable to a low-pressure discharge line (for the forward stroke) and to a branch of a conduit carrying the supply pressure (for 52 US. (:1 91/246, 91/300, 91 /321, the return Stroke) by a lide valve whose shifting is hy- 91/446 draulically controlled by the ram. A throttle valve in [51] 'f 15/16! F01] 25/06, Folb 7/18 the branch conduit leading to the slide valve senses [58] Field of Search 91/246, 300, 321, the Supply pressure and, if that pressure f ll below a 8 446 predetermined level, partly blocks that branch so as to reduce the reverse pressure differential effective dur- [56] References and ing the return stroke whereby the withdrawal of the UNITED STATES PATENTS ram from an impact-receiving tool is delayed so that 501,959 7/1893 Rawlings 91/446 the impact frequency decreases, thus reducing the 1,303,705 5/1919 Manse 91/321 mand upon the source and providng more time for the 3,232,176 2/1966 Henning et al. 91/321 buildup of the requisite working pressure. 3,552,269 1 1971 Arndt 91/300 3,552,270 1 1971 Lange 91 300 7 Chums, 3 Drawing Figures 1& 75 1 P0 4 1 50 Z W -126 '1 17 E F V2 4- 9 1 F L- R 5 I0 20 8 18 t HYDRAULIC PERCUSSION DEVICE WITH PRESSURE-RESPONSIVE CONTROL OF IMPACT FREQUENCY V 1. FIELD OF THE INVENTION 2. DESCRIPTION OF THE PRIOR ART Impact tools of the general type described hereinafter use principles set forth in my prior US. Pat. Nos. 3,322,210, issued and 3,552,269.

Such an impact tool has a case-hardened or similarly strong differential piston or ram which can be reciprocated into or out of engagement with an impact-. receiving element such as a chisel or drill. The differential piston has a pair of axially oppositely directed faces or lands of different sizes (effective areas), the face of larger area being turned toward the impact-re-ceiving tool. Each face confronts a respective fluid chamber which is-the case of the smaller face is continuously in fluidic connection with a source of high-pressure fluid. The other chamber, which is the one turned toward the tool, can be connected by a slide valve, controlled by the position of the impact piston, either to the highpressure source in order to retract the piston away from the tool or to a low-pressure discharge line in order to allow fluid pressure in the opposite chamber to drive the piston forwardly against the tool. The piston should be accelerated all the way from its retracted position until it strikes the tool at its maximum velocity in order to impart the greatest. possible amount of energy thereto. Thereafter it is retractedand', when it reaches the position farthest from the tool, the switching is reversed usually by some valve action directly executed by the piston whereby pressure in the other chamber is relieved to send the piston rapidly toward the tool again.

Such devices work quite well as long as one principal requirement is fulfilled: the working pressure must remain fairly high and steady;otherwise efficiency'drops off greatly. When the pressure is too low, both the impact cadence or repetition frequency and the force of the blows drop off. The amount of work done by the device decreases with the cadence, which can be very inconvenient. A weak blow can be totally ineffective in many situations and, in spite of the fact that the device.

seems to be operating, albeit slowly, nothing is accomplished. Such a drop in pressure is unavoidable in many installations, especially where one pump and reservoir are used for several devices.

3. OBJECTS OF THE INVENTION predetermined limit necessary to generate sufficient impact at the normal'striking frequency of the ram.

4. SUMMARY OF THE INVENTION I attain the aforestated objects by the provision of a throttle valve, responsive to the supply pressure of the hydraulic fluid source, in a branch of a high-pressure imput conduit connected to that source, namely the branch through which fluid pressure is applied to the forwardly facing land of the ram in the working position so as to build up a reverse pressure differential across the two lands to return the ram to its rearward position; The throttle valve, on sensing a drop in the supply pressure prevailing in the high-pressure conduit, thus reduces the reverse pressure differential effective during the return stroke-so as to delay the retraction of the ram with consequent reduction in the impact frequency.

According to another feature of my invention, the valve controlling the reciprocation of the ram has a body with a smaller and a larger end face received in .respective fluid cylinders of its housing, the cylinder containing the smaller end face communicating permanently with the aforementioned branch conduit downstream of the throttle valve whereas the other cylinder is alternately connectable by the ram to the highpressure input conduit and to the low-pressure discharge line. As a result, a lowering of the supply pressure acting upon the larger end face is accompanied by a decrease in the countervailing pressure effective at the smaller end face of the valve body.

5. BRIEF DESCRIPTION OF THE DRAWING The above and .other objects, features, and advantages of my invention willbecome apparent from the following description, reference being made to the accompanying drawing in which:

FIG. 1 is a vertical section through the device according to the present invention, with the piston in its rearward position;

FIG. 2 is a view similar to FIG. 1 showing the piston in its working or forwardposition; and

FIG. 3 is a view similar to FIGS. 1 and 2 showing the piston in a partially retracted position.

6. SPECIFIC DESCRIPTION 'A housing 2 is formed with an axially extending bore 3 in which an elongated stepped piston or'ram 1 is vertically reciprocable. This piston is basically cylindrical and formed with two-like-diameter collars lb and 1d separated by a circumferential groove 1c, and a pair of reduced-diameter extremities la and Ie, the latter being of smaller diameter than the former. In this manner the piston has a pair of oppositely directed lands or faces F and F respectively confronting the piston la and 1e and defininga pair of fluid spaces or chambers 3a and 3b. Thus, withequal pressure in the chambers 3a and 3b the piston I will move up into the rearward position shown in FIG. 1.

A pump 25 serves'as a source of fluid pressure, with its output side producing a relatively high hydraulic pressure P and its intake side creating a relatively low hydraulic pressure P A reservoir can be included at the intake side of the pump 25. The supply pressure P continuously acts through an input conduit 14 upon the face F of the piston l to urge it down toward a chisel head 12. The other face F of the piston 1 can have its chamber 3b connected by means of a reversing valve 16 either to a branch 5 of the high-pressure input conduit 14 or to a low-pressure discharge conduit 13 returning to the intake of pump 25.

A control valve 16 has a vertically reciprocable spool-shaped body 8 having a pair of pilot pistons 7 and 6 with respective end faces F and F the latter being larger than the former. The smaller piston 7, received in a cylinder 7 is continuously subjected to the pres sure P in the conduit branch 5 through a leg 5a of this branch whereas the cylinder 6 of the larger piston 6 can be coupled through a passage 4 and the annular chamber 9 defined by the reduced-diameter portion 10 of the piston l to either the high-pressure conduit 14 (FIG. 2) or the low-pressure conduit 13 (FIG. 3). Of course the ends of the main cylinder chamber of valve 16 are both connected to the conduit 13 to allow free movement of the spool 8.

A pressure-responsive,throttle valve 15 is provided in the branch 5 between the conduit 14 and the valve 16. This valve 15 comprises a horizontally reciprocable slider 20 with a pair of piston heads 20', 20" separated by a circumferential groove 24, head 20' having a face F exposed to the supply pressure P,, in conduit 14 whereas head 20 has a face bearing on a compression coil spring 23. When the pressure P is sufficiently high to operate the device in a normal manner, it acts on the slider 20 with sufficient force to push it to the right in FIG. 1 and cause the spring 23 to bottom, thereby allowing virtually unimpeded fluid flow through the branch across a channel 22 registering with groove 24. If, however, this pressure P drops to a level sufficient to permit normal reciprocation of the piston 1, the spring 23 will force the slider 20 to the left, thereby partly blocking the branch 5 at 22 and lowering the pressure P in this branch (and in an extension 5' thereof communicating with it in the alternate valve position shown in FIG. 2) to less than the pressure P,,.

An accumulator communicates with the conduit 13 and a similar accumulator ll communicates the branch 5. My US. Pat. No. 3,322,210,- issued 30 May 1967, describes such accumulators.

The impact device according to my present invention operates as follows:

Initially the apparatus to be in the position of FIG. 1 and fully depressurized; as the pump 25 is actuated and pressure P builds up the piston 1 will start to move downwardly. Simultaneously the fluid below the piston in the chamber 3b will bleed off through line 5 and valve 16, exiting via conduit 13. As the pressure P builds up, the pressure P will follow suit if the pressure P is large enough to open the valve by shifting its slider to the right from the branch-blocking position into which it is urged by biasing spring 23.

FIG. 2 shows how, once the piston 1 comes down and strikes the chisel 12, its collar 1b will clear a circumferential groove 17 connected to conduit 4. This action will allow the fluid under pressure P,, to flow through the conduit 4 and act on the surface F thereby pushing the spool 8 down since the surface F is greater than the surface F,, and since the pressure P cannot exceed the pressure P In the down position this spool 8 connects the lower chamber 3b via extension 5 to the conduit branch 5 to force the piston 1 up, since the surface area of land F is greater than the surface area of land F The pressure-responsive throttle valve 15 is designed to slow the rate at which the piston l and the spool 8 lift so as to lengthen the period of the repetition frequency when pressure P,, is below a predetermined level. Thus, the throttle valve 15 reduces that frequency with a decrease in pressure P but the force with which the piston strikes the tool unaffected by that valve which is bypassed by the conduit 14 connecting the fluid space 3a to pump 25. As long as the pressure P,, is at a level sufficiently high to ensure continuous operation of the device at normal rate, the slider 20 will be pushed back against its spring 23 by the pressure effective on its face F so that the pressure P, in the conduit branch 5 will be virtually at the same level as pressure P,,. In this condition the piston 1 will reciprocate, at its rated speed. Should, however, pressure P,, drop below the level at which it can operate the piston l at full speed with its full power, the slider 20 will move to the left under the effect of spring 23 and restrict the flow into the branch 5, extension 5' and leg 5a. The pressure P will therefore be lower than the pressure P,, so that it will take longer for the piston 1 to rise. In many cases the piston 1 will remain in its forward (FIG. 2) position until pressure P very nearly equals pressure P and even then will rise only at a speed related to the pressure differential P I" In FIG. 3 the piston 1 is shown in an intermediate position, remote from tool 12, in which the collar 1d clears a groove 18 which it obstructs in the fully retracted position. The annular chamber 9 now interconnects the two circumferential grooves 17 and 18 respectively connected to the conduit 4 and to the outlet 13 so that the pressure in cylinder 6 above the piston 6 is relieved. Since the pressure P downstream of value 15 is always higher than the discharge pressure P the spool 8 will be lifted back into the position illustrated in FIG. 1, thereby allowing the cycle to start all over again.

The speed at which the spool 8 lifts in this last stage is also determined by the pressure differential P P a leftward shift of throttle 15 being thus effective to retard also the upward motion of valve body 8 which must precede the next descent for ram 1 since it establishes a drainage connection between fluid space 3b and discharge line 13.

I claim:

1. A hydraulic percussion device comprising:

a housing provided with a bore;

a ram reciprocable within said bore between a rearward position withdrawn from an impact-receiving element and a forward positon proximal to said element, said ram being provided with a relatively small rearwardly facing land confronting a first fluid space and with a relatively large forwardly facing land confronting a second fluid space;

a source of high-pressure hydraulic fluid;

conduit means permanently connecting said source to said first fluid space and carrying fluid at the supply pressure of said source;

valve means controlled by said ram for connecting said second fluid space to a low-pressure discharge line in said rearward position wherby the fluid pressure in said first fluid space is effective to drive said ram forwardly toward said element, said valve means being operative in said forward position to connect said second fluid space to a branch of said conduit means for developing a reverse pressure differential across said lands to return said ram to said rearward position; and

throttle means in said branch responsive to said sup ply pressure for reducing the reverse pressure differential effective during rearward motion of the ram by partly blocking said branch upon diminution of said supply pressure below a predetermined level, thereby delaying the return of said ram to said rearward position.

2. A device as defined in claim 1 wherein said valve means comprises a body having a smaller end face in a first fluid cylinder, communicating permanently with said branch downstream of said throttle means, and having a larger end face in a second fluid cylinder, the latter being alternately connectable by said ram to said conduit means and to said discharge line.

3. A device as defined in claim 2 wherein said ram is effective to connect said first fluid cylinder to said conduit means in said forward position and to said discharge line in an intermediate position remote from said element.

4. A device as defined in claim 1 wherein said throttle means comprises a slider provided with biasing means urging same into a branch-blocking position.

5. A device as defined in claim 4 wherein said biasing means comprises a compression spring bearing upon one end of the slider, said slider having its opposite end permanently subjected to the supply pressure in said conduit means.

6. A device as defined in claim 1 comprising a pressure accumulator communicating with said branch.

7. A device as defined in claim 6, comprising a further pressure accumulator communicating with said discharge line.

23 2 33 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No, 317740502 Dated 27 November Inventor s) Ftiedri'ch-Karl ARMJ'I It is certified that error' appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

In the heading, after line insert:

-- E30] Foreign A plication Priority Data May 20, 1970 Germany P 20 24 501.6

Signed and sealed this 21st day of May 1974.

' (SEAL) Attest:

EDWARD M.FLETCHER,JR. C. MARSHALL DANN Attesting Officer Commissioner of Patents 

1. A hydraulic percussion device comprising: a housing provided with a bore; a ram reciprocable within said bore between a rearward position withdrawn from an impact-receiving element and a forward positon proximal to said element, said ram being provided with a relatively small rearwardly facing land confronting a first fluid space and with a relatively large forwardly facing land confronting a second fluid space; a source of high-pressure hydraulic fluid; conduit means permanently connecting said source to said first fluid space and carrying fluid at the supply pressure of said source; valve means controlled by said ram for connecting said second fluid space to a low-pressure discharge line in said rearward position wherby the fluid pressure in said first fluid space is effective to drive said ram forwardly toward said element, said valve means being operative in said forward position to connect said second fluid space to a branch of said conduit means for developing a reverse pressure differential across said lands to return said ram to said rearward position; and throttle means in said branch responsive to said supply pressure for reducing the reverse pressure differential effective during rearward motion of the ram by partly blocking said branch upon diminution of said supply pressure below a predetermined level, thereby delaying the return of said ram to said rearward position.
 2. A device as defined in claim 1 wherein said valve means comprises a body having a smaller end face in a first fluid cylinder, communicating permanently with said branch downstream of said throttle means, and having a larger end face in a second fluid cylinder, the latter being alternately connectable by said ram to said conduit means and to said discharge line.
 3. A device as defined in claim 2 wherein said ram is effective to connect said first fluid cylinder to said conduit means in said forward position and to said discharge line in an intermediate position remote from said element.
 4. A device as defined in claim 1 wherein said throttle means comprises a slider provided with biasing means urging same into a branch-blocking position.
 5. A device as defined in claim 4 wherein said biasing means comprises a compression spring bearing upon one end of the slider, said slider having its opposite end permanently subjected to the supply pressure in said conduit means.
 6. A device as defined in claim 1 comprising a pressure accumulator communicating with said branch.
 7. A device as defined in claim 6, comprising a further pressure accumulator communicating with said discharge line. 